In many communication systems, a channel bit error rate (BER) is used as a figure of merit. One type of communication system standard is Synchronous Optical Network (SONET), wherein a receiver, i.e. a line terminating device, must determine the channel BER quickly, and must react in the event the BER increases above defined error thresholds. Each receiver must thus be able to measure the channel BER, and indicate when the channel BER has exceeded a predetermined threshold.
In SONET systems, a sliding window is used, wherein the number of error bits received during the last N received bits is calculated, N being the window size. The number of bit errors during the window can be used to statistically estimate the channel BER. Alternatively, the number of bit errors during the window can be compared to a threshold value. If the threshold is exceeded, a BER monitoring circuit indicates that the channel BER has exceeded the threshold. This calculation is repeated for each bit received.
A significant problem exists in utilizing a sliding window. Error statistics of each bit in the window must be stored. Since the window size can get very large, it has been found to be cumbersome to implement the above in hardware.